5.2 Electron Configurations • Electron Configurations • Rules for writing the electron configurations of elements?
5.2 Electron Configurations • The ways in which electrons are arranged in various orbitals around the nuclei of atoms are called electron configurations. • Three rules—the aufbau principle, the Pauli exclusion principle, and Hund’s rule—tell you how to find the electron configurations of atoms.
5.2 Electron Configurations • Aufbau Principle • According to the aufbau principle, electrons occupy the orbitals of lowest energy first. In the aufbau diagram below, each box represents an atomic orbital.
5.2 Electron Configurations • Pauli Exclusion Principle • According to the Pauli exclusion principle, an atomic orbital may describe at most two electrons. To occupy the same orbital, two electrons must have opposite spins; that is, the electron spins must be paired.
5.2 Electron Configurations • Hund’s Rule • Hund’s rule states that electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible.
5.2 Electron Configurations • Orbital Filling Diagram
5.2 Exceptional Electron Configurations • Exceptional Electron Configurations • Why do actual electron configurations for some elements differ from those assigned using the aufbau principle?
5.2 Exceptional Electron Configurations • Some actual electron configurations differ from those assigned using the aufbau principle because half-filled sublevels are not as stable as filled sublevels, but they are more stable than other configurations.
5.2 Exceptional Electron Configurations • Exceptions to the aufbau principle are due to subtle electron-electron interactions in orbitals with very similar energies. • Copper has an electron configuration that is an exception to the aufbau principle.
5.2 Section Quiz. • 5.2.
5.2 Section Quiz. • 1. Identify the element that corresponds to the following electron configuration: 1s22s22p5. • F • Cl • Ne • O
5.2 Section Quiz. • 2. Write the electron configuration for the atom N. • 1s22s22p5 • 1s22s22p3 • 1s22s1p2 • 1s22s22p1
5.2 Section Quiz. • 3. The electron configurations for some elements differ from those predicted by the aufbau principle because the • the lowest energy level is completely filled. • none of the energy levels are completely filled. • half-filled sublevels are less stable than filled energy levels. • half-filled sublevels are more stable than some other arrangements. `